Identification of males contained within Japanese quail ( <i>Coturnix japonica</i> ) eggs: Is heat transfer a determining factor?

Both wild birds and commercial poultry species have the typical sex ratio at birth, which means that about half of the males are unable to produce eggs. Relationship between embryo sex and egg geometrical and physical properties is one of the most reexamined assumptions. The aim of this study was to identify the relationship between the geometric and physical parameters of Japanese quail ( Coturnix japonica ) eggs and the sex of the embryos contained within them. The various parameters tested included egg shape, asymmetry and conicity indices, volume, surface area, weight, densities of the whole egg and its contents, and several parameter combinations based on these variables. Of these, only heat transfer index showed significant differences between the groups of male and female eggs on Day 5 during incubation. It was hypothesized that the value of this coefficient is related to the stage of embryo development and the intensification of metabolic rate. This may differ significantly between male and female embryos. Differences in heat transfer values provided accurate information about the potential culling of approximately 18% of the total number of eggs containing male embryos. Suggestions were made for improving the conditions for similar studies aimed at increasing the efficiency of egg sexing.